Only one reason to snap loose. No grip at the inside rear and the outside rear is being worked beyond what it can give and the front has grip.
When you drop down weight jacking your causing the inside rear to help hold you in by not allowing it unload as much and the hard steering is because you still have grip up front. At that time your wanting to accelerate but your killing it because your still turning and fighting the back to go where you want to go, with an engaged inside rear.
Or in other words push in loose out and in your case it’s a whole ton of loose out. Your telling us you can’t fix it with adjustments because the adjustment your trying to fix it with, puts or keeps the inside rear engaged too much.
If you cannot truly fix it with adjustments you have to fix it with your driving. Your either driving in too far or cutting off the corner. If your driving in too far, then it’s the thing won’t turn and when you slow to make it turn, you have too much turning left to do and you break the back loose. But I don’t see that as your driving problem.
I see your driving problem to be your chopping off the corners. That means your pretty much driving a straight line down at and by the corner, and then trying to make it turn. It can’t because you did not get enough of your turning done prior to that point on the track. But since you have grip up front the front holds and your outside rear lets loose. Your driving fix is one of two things. One, you can try entering higher to give you room to complete more turning through the corner, before you get to your apex an on out. The second way to fix it if you can’t manage to change your line, is to brake and then roll a little in an arc to complete more of your turning, before you consider an apex point. Either way you have to get more initial turning done, before choosing an apex. If you don’t and have too much turning left, your either going to be a pig grinding off speed with the fronts fighting the somewhat engaged inside rear or you will snap loose.